Navigation at sea and in waterways is inherently dangerous. When navigating, the movement and identity of other ships in the vicinity of a vessel is critical to making decisions to avoid collision and other dangers (e.g., shoals, reefs, bars, or rocks). Historically, navigators rely on a number of aids to prevent collision, such as visual observation (e.g., unaided, binoculars, night vision), audio exchanges (e.g., whistle, horn, radio), radar, and/or an Automatic Radar Plotting Aid (ARPA). However, a lack of positive identification of objects indicated by displays, time delays associated with processing information, and limitations of radar for observing and calculating the action and response of nearby vessels, all may prevent timely action to avoid a collision.
The International Maritime Organization (IMO) and the International Telecommunications Union (ITU) has developed an aid to navigation known as the Automatic Identification System (AIS). AIS was created to improve the navigation and monitoring of ocean going vessels for security and safety reasons. AIS is a system used by ships and traffic services to identify and locate vessels. AIS helps to resolve the difficulty noted above of identifying ships when, for example, visual communications are not easily established (e.g., in fog, at a distance, obstructing terrain features) by allowing ships to exchange information with all other nearby ships and VTS stations.
The AIS works by integrating a standardized VHF transceiver system with an electronic navigation system, such as a LORAN-C or Global Positioning System receiver, and other navigational sensors on board ship (e.g., gyrocompass and rate of turn indicator, among others). Although AIS may be used in navigation to avoid collisions, due to the limitations of radio characteristics of the system (and because not all vessels are equipped with AIS), the system is primarily used to determine risk of collision rather than as an automated collision avoidance system.
AIS also provides data exchange between ships and between ships to shore. While requirements of AIS are only to display very basic text information, the data obtained can be integrated with a graphical electronic chart or a radar display to provide consolidated navigational information on a single display. AIS is mandated by international law for ships engaged in international traffic over 300 tons or more. However, in the near future, AIS will be expanded to include all ships of 500 tons or more in international voyages and possibly others.